The present invention relates to a vehicular direct-current three-wire electrical system which is suitably connected for the wiring and control of both a system for charging a storage battery with the rectified output of an alternating-current generator mounted on the vehicle and driven by an internal combustion engine and the starter system of that internal combustion engine.
First of all, a prior art system of the above-specified type will be described with reference to FIG. 1. In FIG. 1, reference numberal 1 indicates an alternating-current generator which is mounted on a vehicle (not shown) and which is driven by an internal combustion engine (not shown). The a.c. generator is constructed of armature coils 101 in the three-phase star-connection and a field coil 102. Numeral 2 indicates a three-phase full wave rectifier for rectifying the a.c. output of the a.c. generator 1. The rectifier 2 has a plus output terminal 201 and a minus output terminal 202.
Moreover, numeral 3 indicates a voltage regulator for controlling the output voltage of the a.c. generator 1 so as to equal a predetermined value by controlling the current flowing through the aforementioned field coil 102. A first storage battery 5 is connected between the plus and minus output terminals 201, 202 of the aforementioned three-phase full-wave rectifier 2, and a key switch 9 is connected between the plus terminal of the first storage battery 5 and the voltage regulator 3.
An electric load 7 is connected in parallel with the first storage battery 5, which has its plus and minus terminals connected to each other through the drive coil 401 of an electromagnetic relay 4. The electromagnetic relay 4 is provided for switching the connection between the first storage battery and a second storage battery 6 from series to parallel and vice versa.
The electromagnetic relay 4 is constructed of the drive coil 401, a first movable contact 402, a second movable contact 402, a first normally open stationary contact 404, a second normally open stationary contact 405, a first normally closed stationary contact 406 and a second normally closed stationary contact 407.
The first movable contact 402 is connected to the plus terminal of the first storage battery 5, and the second movable contact 403 is connected to the minus terminal of the second storage battery 5. The first and second movable contacts 402 and 403 are made coactive with each other. The plus terminal of the second storage battery 6 is connected with the first normally closed stationary contact 406 and further through the starting motor 8 of the internal combustion engine with the minus terminal of the first storage battery 5. On the other hand, the second normally closed stationary contact 407 is connected with the minus terminal of the first storage battery 5.
The operation of the prior art system thus arranged will now be described. Initially, when the key switch 9 is closed upon starting of the internal combustion engine, a field current is supplied from the first storage battery 5 through the key switch 9 and the voltage regulator 3 to the field coil 102 so that a field magnetomotive force is generated.
Next, when the operating switch 10 is closed, the drive coil 401 of the electromagnetic relay 4 is energized to drive the first movable contact 402 and the second movable contact 403. As a result, the first movable contact 402 is open-circuited with respect to the first normally closed stationary contact 406 but is closed with respect to the first normally open stationary contact 404. Simultaneously, the second movable contact 403 is coactively open-circuited with respect to the second normally closed stationary contact 407 but is closed with respect to the second normally open stationary contact 405. As a result, the starting motor 8 is supplied with the series-connected voltage of the first and second storage batteries 5 and 6.
When the starting motor 8 rotates in this state to start the internal combustion engine, an a.c. output is induced in the armature coils 101. This a.c. output is full-wave rectified by the three-phase full-wave rectifier 2 to charge the first storage battery 5. The aforementioned rectified output is controlled to equal the predetermined value by the voltage regulator 3.
When the starting switch 10 is opened after the start of the internal combustion engine, the first and second storage batteries 5 and 6 are connected in parallel with each other so that they are simultaneously charged by the a.c. generator 1 and the three-phase full-wave rectifier 2.
The aforementioned system of the prior art requires the electromagnetic relay 4 for switching between the series and parallel connections between the first and second storage batteries 5 and 6, and thus has drawbacks in that its lifetime is shortened, and that its reliability is degraded.